Effects of inorganic anions and cations on oxygen binding of haemoglobin from Arenicola marina (Polychaeta)

Abstract

1. 1. The influence of inorganic salts on oxygenation properties of haemoglobin of Arenicola marina was studied. 2. 2. In contrast to the tetrameric mammalian haemoglobins the oxygen affinity of Arenicola haemoglobin is increased by salts. The results suggest that the effects of salts on the p 50 values are predominantly determined by the cationic salt components in solution. Divalent cations produce greater facilitation of oxygen binding than monovalent ones, but the effective oxygen affinities are not determined solely by ionic strength. Increasing salt concentrations decrease the Bohr effect of the pigment at physiological pH conditions. 3. 3. Added salt increases the haem-haem interaction coefficient n. This effect is greater for divalent than monovalent cations at the same molar concentration. At critical concentrations of chloride salts, n shows distinct maxima not found with sulphate salts, indicating a contributory role of chloride anions in determining haem-haem interaction. 4. 4. Specimens of Arenicola subjected to varying salinities reveal poor electrolyte regulation, indicating that environmental salt concentrations will interact directly with the extracellular haemoglobin. 5. 5. The data are compared with salt influences in mammalian haemoglobin and discussed in terms of the possible molecular mechanisms involved and their possible significance in the natural habitat of the animal.